The present invention relates to a process for producing refractory material and more in particular to an improved process to produce refractory material by sintering.
Refractory materials such as the oxides of magnesium, calcium, aluminum, and zicronium are conventionally manufactured by heating the raw material to achieve decomposition and densification.
One general process for producing a refractory material, such as sintered magnesium oxide (periclase), involves two seperate heating steps in which the decomposition and densification steps are separated and optimized. This optimization is designed to increase the bulk density of the refractory material.
A typical two-stage process, such as that used to produce sintered magnesium oxide, normally employs an initial heating step at about 900.degree. C using a multiple-hearth calciner for decomposition and a second heating step employing either a shaft or rotary kiln for densification. Heating for densification normally occurs at temperatures in excess of 1700.degree. C and is generally referred to as sintering. The normal two-stage process usually includes a separate compacting process prior to sintering. Generally, the calcined magnesium oxide is formed into seperate briquette compacts by mechanical compaction.
One general description of a two-stage process for producing sintered magnesium oxide is shown in U.S. Pat. No. 3,060,000.
In the known process of using a shaft or rotary kiln for sintering, it has been necessary to fire the kiln at very high temperatures in order increase the bulk densities of the refractory material. However, the bulk density of the product produced has oftentimes not been as high as desired. It is, therfore, desirable that an improved sintering process for producing refractory material with increased density be developed.